PHYLOGENY 



Figure 30. Electron Micrographs of Viruses. 1. V'accinia \iius. 2. liilluciiza \iius. 

 3. Tobacco mosaic virus. 4. Potato mosaic virus. 5. Bacteriophages. 0. Sliope papilloma 

 virus. 7. Southern bean mosaic virus. 8. Tomato bushy stunt \ irus. ( From V^illee, 

 "Biology, The Human Approach," 3rd Ed., W. B. Saunders Co., ]^)57.) 



ther mutations niitiht then lead to the aecunuilation oi metabolites around 

 the chromosomes, and the complex so produced could then be regarded 

 as an exposed nucleus. Bacteria in general are sometimes regarded as rep- 

 resenting this level of organization. Next, cytoplasm miglit be accpiired 

 but not s(>parated from the nuclear material, as in the blue-gr(>en algae, 

 or in th(> larger bacteria. Finally, mutation could then result in the forma- 

 tion of typical cells with micleus and c\'toplasm separatc>d by a membrane. 

 Within such cells lie all of the potentialities of higher plants and animals. 

 The possible details of such a chemical evolution of the most elementary 

 forms of life have been particularly well worked out b\ Ojiarin, and his 

 account will b(^ followed for the most part below, it ma\' be noted at the 

 outset that this is actually a special case of spontaneous generation, though 

 it is a plausible one because it does not involve direct origin of compli- 

 cated organisms from nonliving matter. 



92 



